Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $219.81   9.613%   $240.9403   $240.94   $240.95   $240.90  
  Purchase #2 $195.35   6.717%   $208.4717   $208.47   $208.45   $208.50  
  Purchase #3 $93.53   13.488%   $106.1453   $106.15   $106.15   $106.10  
  Purchase #4 $196.96   9.320%   $215.3167   $215.32   $215.30   $215.30  
  Purchase #5 $243.92   6.183%   $259.0016   $259.00   $259.00   $259.00  
  Purchase #6 $41.93   13.745%   $47.6933   $47.69   $47.70   $47.70  
  Purchase #7 $152.87   8.829%   $166.3669   $166.37   $166.35   $166.40  
  7 purchase totals = $1,144.37       $1,243.9358   $1,243.94   $1,243.90   $1,243.90